1. Field of the Invention
The present invention relates to an intake manifold for a multi-cylinder engine and particularly, to an improvement in a structure of blow-by-gas passage in the same.
2. Description of the Related Art
A known intake manifold for a multi-cylinder engine is designed such that intake tubes are bound to groups or a single bundle to avoid interference between intake air flows and to distribute the air-flows uniformly.
Such a conventional intake manifold 1 comprises, as shown in FIG. 5, a collector 2 formed by aluminum die casting, a plurality of intake tubes 3 made of aluminum pipes, and an intake tube mount 4 formed by aluminum die casting for fixedly mounting the intake tubes 3 to the engine. The intake tubes 3 are bent to desired shapes and joined to the collector 2 and the intake tube mount 4. One end of the collector 2 is connected to a blow-by gas tube 5. when the cylinders are negatively pressurized, The blow-by gas tube 5 serves to feed back to the engine a mist of blow-by gas (oil mist) which has leaked through gaps at the piston rings to the crank case and contains some lubricant oil (and thus should not be discharged directly to the outside). The blow-by gas from the blow-by gas tube 5 is fed via an inner space 6 in the collector 2 to the intake tubes 3 as shown in FIG. 6.
Another type of a known intake manifold has a structure shown in FIGS. 7 and 8, in which a communicating tube 7 communicates with the intake tubes 3 and is mounted as a branch to intermediate portions of the intake tube 3 for taking a blow-by gas via a tube 8 from the engine. The intake tubes 3 and the communicating tube 7 are made of cast iron. The communicating tube 7 is joined to the intake tubes 3 by pipes 9.
The first known type of intake manifold 1 discussed above permits the single blow-by gas tube 5 to be connected to the inner space 6 of a considerable size to which the intake tubes 3 are also connected. This may cause blow-by gas to flow mostly into some of the intake tubes 3 located adjacent to the blow-by gas tube 5. Therefore, only a small amount of blow-by gas flows into the other intake tubes 3 located far from the blow-by gas tube 5, hence hardly providing uniform distribution of the blow-by gas to the intake tubes 3. If the intake manifold 1 includes pipes each connected to their respective intake tube 3 for distributing the blow-by gas uniformly, its construction will be intricate thus increasing the cost.
The second known type of the intake manifold has the communicating tube 7 mounted to the intermediate portions of the intake tubes 3 and is complicated in the structure. Also, because the communicating tube 7 is joined by the intake tubes 3 by the pipes 9, measures against vibration of the pipes 9 are needed.